A typical fuel system has a fuel pump which delivers fuel at a rate higher than that required for the operation of the engine. Excess fuel downstream of the fuel pump is bypassed usually by a fuel pressure regulator of some sort, and returned to a fuel reservoir upstream of the fuel pump such as the main fuel tank or a reservoir defined within a fuel pump module or a reservoir defined by a liquid-vapor separator. In some applications a fuel pressure regulator is disposed immediately downstream of the fuel pump to bypass the excess fuel delivered by the fuel pump. In other applications, the fuel pressure regulator is located adjacent the fuel rail on the engine to bypass excess fuel at the fuel rail. In these latter systems, because the fuel is routed closely to the engine before being bypassed, it becomes heated and when returned to a reservoir within the fuel system, this heated return fuel generates fuel vapor within the fuel system which is volatile and hazardous to the environment, detrimental to engine operation and which also decreases the efficiency and life of the fuel pump in use.
U.S. Pat. No. 5,309,885 discloses a marine engine fuel system which routes return fuel to a liquid-vapor separator which is in heat exchange relationship with a cooling chamber through which cold water is circulated to absorb some of the heat from the contents of the liquid-vapor separator, to thereby reduce the amount of vapor therein. However, especially at idle conditions, when an increased amount of fuel is being bypassed and the return fuel is not cooled until after it is discharged into the separator and its pressure is reduced, increased vapor generation occurs requiring an increased volume and hence increased size of the liquid-vapor separator and the water cooling chamber.